The present invention comprises an improvement over the encoder-decoder shown by Canadian patent 935,581 to E. Pinede et al issued 10/10/73.
Continuously variable sloped delta modulation is generally known in the art. For example, the above noted Canadian patent shows an encoder in which voice signals are fed to the CVSD input, which passes signals in the voice frequency range. A comparator, which may be in the nature of a difference amplifier, compares the voice frequency signal with a digital approximation of that signal. The output of the comparator is gated through a clocked sample gate. The sample is stored in a three-bit shift register, a code being formed responsive to the amplitude of the voice sample. An exclusive OR gate is enabled when three bits are simultaneously present in the shift register. The output of the exclusive OR gate is weighted in a lowpass syllabic filter and then applied to a pulse amplitude modulator (PAM). The PAM sample is integrated and fed back to the comparator to provide the digital approximation for comparison purposes.